Question

Ionic mobility of which of the following alkali metal ions is lowest when aqueous solution of their salts are put under an electric field ?

• A. K
• B. Rb
• C. Li
• D. Na

Answer 1

Answer: (C)

Li

Answer 2

Li $^{+}$ being smallest, has maximum charge density $\therefore Li ^{+}$ is most heavily hydrated among all alkali metal ions. Effective size of $Li ^{+}$ in aq solution is therefore, largest.

$\therefore$ Moves slowest under electric field.